1. Field of the Invention
The present invention relates to a method of condensing a liquid solution in a plant adapted to evaporation, more particularly a multi-stage plant adapted to an evaporation of milk, a mechanical compression of the treatment vapour being carried out so as to have the the former regain its initial temperature and pressure, is used in the subsequent stage with a lower boiling point of the product, in view of successively increasing the dry substance contents of the product by evaporation.
2. Description of the Prior Art
It is known per se that the use of a single-stage compressor in a similar method will cause the rise in pressure and temperature to be restricted, so that in multi-stage evaporators the heating surface has to be enlarged. Consequently the liquid load upon the pipe(s) will become insufficient so that dry boiling will occur in some parts of the plant, whilst a pollution (crustation) of the heat exchanging surfaces (the pipes) cannot possibly be avoided. These phenomena will especially occur in the last stages whereat, due to the higher dry substance contents, the heat transfer coefficient will be decreased, so that a greater surface will be required.
Efforts have been made to overcome this problem by dividing (splitting up) the pipes into a number of sections (so-called passes) and by having these sections pass the product connected in series. This causes the load on the pipe(s) to be so increased that any danger of dry boiling is restricted to a minimum. Said division, however, will substantially increase the costs of investment, due to the necessity of providing additional housings, pumps, lines and drop separators. Although a higher initial level of temperature and pressure of the treatment vapor can actually be obtained by the use of a multi-stage compresser, the costs of investment will also be considerably increased by the latter measure.